rust - Conditional compilation with a if let enum matching which consists of one item -

i have following enum:

pub enum game {     match(gameworker),     #[cfg(feature = "cups")]     cup(cupworker), } 

so, enum consists of 1 item if cups feature disabled. code below match compiles okay in place use if lets on matching enum there error:

working match:

fn clear(&mut self, silent: bool) {     match *self {         game::match(ref mut gm) => gm.clear(silent),         #[cfg(feature = "cups")]         game::cup(ref mut c) => c.clear(silent),     } } 

if let leads compile error:

let m: &mut game = game::match(...); if let game::match(ref mut gamematch) = *m {     // ... } 

error:

error[e0162]: irrefutable if-let pattern    --> src/game.rs:436:32     | 436 |                         if let game::match(ref mut gamematch) = *m {     |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ irrefutable pattern 

minimal example

is there way allow such if lets ? construction somewhy not allowed use it, don't understand why. shown above, match construction works okay in same case. in personal opinion here should silenceable warning instead of error.

if let expects refutable pattern, similar how if expects bool. can't write if () { }, though () "valid" in sense. if had if () {} else { something_else } statically known else cannot occur.

arguably if true { } statically known, there's difference: condition bool, has 2 values, if statically know value, type still offers multiple variants.

with if let it's same, can use user defined types instead of bool. if enum has multiple variants, can't statically decide if let taken. if enum has single variant, know fact if condition true, if had else branch, not make sense @ exist.